The present disclosure relates to image readers and image processing apparatuses, and more particularly to an image reader which reads an image of a document and an image processing apparatus which includes such an image reader.
Image processing apparatuses, typified by digital multifunctional peripherals and the like, include an image reader which reads an image of a document. The image reader reads images of a plurality of sheets of documents set on an auto document feeder (ADF), or reads an image of a document placed on a platen. On the basis of the image read by the image reader, the image processing apparatus performs image processing or forms an image in an image forming unit.
The image reader uses a reading unit called a carriage, equipped with an image sensor, to read an image of a document. The carriage is disposed in a space under the platen, and is movable in a so-called sub-scanning direction. The carriage irradiates a document with light emitted from an exposure lamp, and reads an image of the document by using the image sensor. In the case of reading images of documents set in the ADF, the carriage stops at a reading position at which it reads an image of a document while the document is passing (hereinafter, this position will be simply referred to as “reading position”) in the sub-scanning direction. The ADF feeds documents sequentially to the reading position such that one document passes through the position at a time. The carriage reads images of the plurality of sheets of documents while they are passing through the position, by using the image sensor included in the carriage. On the other hand, in the case of reading an image of a document placed on the platen, the carriage, while moving in the sub-scanning direction, irradiates the document placed on the platen with light from the exposure lamp and collects the reflected light to thereby read the image of the document by using the image sensor.
For such a carriage configured to move or stay in a prescribed position while reading an image as described above, a home position (hereinafter, also simply referred to as “HP”) is set which becomes a reference position of the carriage. For example, when a sleep mode as an energy-saving mode is cleared in an image reader, the carriage is moved to the HP, as an initialization operation of the image reader. Thereafter, with the HP as the reference position, the carriage is moved to the reading position for reading images of the documents fed by the ADF, or to the position where it starts reading an image of the document placed on the platen. This configuration enables the carriage to start reading from an appropriate position, irrespective of where the carriage was stopped after the previous image reading operation, thereby ensuring an appropriate image reading operation.
A technique related to such an image reader having a HP set therein is conventionally known. In the conventional image reader, it is configured such that the carriage is placed in the home position at the time of reading an image of a document. The carriage, placed in the home position, is then caused to move to a position where shading correction is carried out or to a position where an image of a document is read. The carriage is equipped with a light shield plate, and a photo interrupter (PI) sensor is provided in the main body. In order to confirm the position of the carriage, first, the position of the carriage at the time when the light shield plate has blocked the light directed to the PI sensor is detected. Then, on the basis of the detected position, the carriage is moved to the home position. With this configuration, however, a relatively expensive PI sensor is indispensable, leading to a complicated mechanism and increased cost.
There is also conventionally known an image reader which is configured, in order to reliably guide a carriage to a prescribed home position in an initialization operation, to detect a positioning mark at the time of initialization and drive a carriage-holding unit by a driving unit to guide the carriage-holding unit to the home position. In this conventional technique, instead of providing a PI sensor, an image sensor, originally for reading an image, is used to detect the positioning mark to thereby recognize the position of the carriage. With such an image reader, however, light from the exposure lamp may get into a user's eyes, making the user feel uncomfortable with the glare.